Voltage regulator



Oct. 18, 1955 N. SILVER ET AL VOLTAGE REGULA'ITOR Filed June 21, 1954 2Sheets-Sheet 1 FIG. I /22 sa a -ANTIHUNT ANTIHUNT CONTROL'/ FIG. 2

NATHANIEL SiLVER DONALD W. TANNER INVENTORS ATTORNEY Oct. 18, 1955 N.SILVER ETAL 2,721,304

VOLTAGE REGULATOR Filed June 21, 1954 2 Sheets-Sheet 2 FIG. 4 20 f2D.G.BIA$- |Q CONTROL' SUPPLY ANTIHUN OONTROL/ NATHANIEL SILVER DONALD W.TANNER INVENTORS ATTORNEY United States Patent O VOLTAGE REGULATORNathaniel Silver and Donald W. Tanner, Stamford, Conn., assignors toSorensen & Company, Inc., Stamford, Conn.

Application June 21, 1954, Serial No. 437,938

4 Claims. (Cl. 321--19) of voltage values.

Many types of voltage regulators have been designed and used whichemploy electron discharge devices such as triodes and pentodes inamplifier circuits in order to produce a control current which can beapplied to a saturable reactor and vary the impedance in a series orparallel circuit to control the output voltage. Other voltage regulatorsuse a single transformer arrangement, the core of which is partiallysaturated, for voltage regulation without the use of amplifier circuits.These latter regulators have not produced good regulation, the outputvoltage varying several percent when the input voltage is varied over arange of plus or minus ten percent. The present invention employs twotransformers, the core in each being operated at a value of magneticflux which partially saturates the core. The use of two transformersproduces a regulation across the load which is a considerableimprovement over the prior art and the absence of electron dischargedevices eliminates the failure due to broken filaments, short circuitedelements within the tube, and loss of vacuum.

One of the objects of the invention is to provide an improved voltageregulator which avoids one or more of the disadvantages and limitationsof prior art arrange ments.

Another object of the invention is to provide an accurate voltageregulator which will have long life and not be subject to the failureswhich are generally inherent in regulators containing electron dischargedevices.

Another object of the invention is to provide a voltage regulator whichis able to withstand considerable vibration and mechanical shock withoutchanging its operating characteristics.

Another object of the invention is to simplify the construction andassembly of voltage regulators.

The invention comprises an alternating current supply for two saturablecore transformers. One transformer transmits power to a load circuitthrough two rectifier units, the amount of power transmitted dependingupon the reactance of the power windings and the saturation of the coreWithin these windings. The magnetic saturation is controlled by fourcontrol windings, one of which is a control winding which is connectedto the second or control transformer. A direct current bias winding isemployed to maintain the average steady magnetic flux at a partiallysaturating value. A third winding is coupled through a capacitor to theoutput terminals and eliminates hunting. A fourth winding is connected2,721,304 Patented Oct. 18, 1955 directly to a winding on the controltransformer and constitutes an alternating current bias control. Thiswinding effectively controls the magnetic impedance of the core whichholds the four control windings. Variations of output voltage are sensedby a four-armed Wheatstone bridge which contains two resistors inopposite bridge arms each having a resistance which does not vary withapplied voltage and two tungsten filament lamps also in opposite arms,each producing a resistance which varies considerably with the appliedvoltage. The output of this bridge is applied to a control winding inthe second transformer. The second transformer contains two currenttransmitting windings which are connected in series with rectifier unitsand the control winding on the first transformer. The second transformeralso includes an anti-hunt winding which is coupled to the outputcircuit through a capacitor.

An alternate arrangement of the voltage regulator described aboveincludes the components as described except that the alternating currentbias winding is replaced by a short circuited winding which effectivelyeliminates the alternating magnetic flux from the middle portion of thetransformer core.

For a better understanding of the present invention, together with otherand further objects thereof reference is made to the followingdescription taken in connection with the accompanying drawings.

Fig. 1 is a schematic diagram of connections of one embodiment of theinvention.

Fig. 2 is a partly schematic drawing showing an alternate arrangement ofthe core material for either one of the two transformers shown in Fig.1.

Fig. 3 is another alternate arrangement of core material.

Fig. 4 is another schematic diagram of connections similar to Fig. l butshowing an alternate circuit arrangement.

Referring now to Fig. l a supply transformer 10 includes a primarywinding 11 having terminals 12, 13 which are to be connected to analternating current supply line which may vary considerably in voltage.A secondary winding 14 includes a tap at its mid-point which isconnected to the negative terminal 15 of the load circuit. The terminalsof winding 14 are connected to two power windings 16 and 17 which areplaced on two portions of a shell type transformer core 18. The otherends of windings 16 and 17 are connected in series with rectifier units20 and 21, the negative terminals of these rectifiers being connectedtogether and to a filter circuit 22 which is designed to eliminate thepulsating components of the rectified power so that only direct currentmay be available at terminals 23 and 15 which are to be connected to anexternal load 24.

A second secondary winding 25 is also part of transformer 10 and has atap at its mid-point which is connected in series with a winding 26 onthe center leg of core 18. This winding 26 is the control winding andvariations of current in this winding change the saturation of the core18 and produce a varying reactance value in winding 16 and 17 therebycontrolling the output voltage across load 24. The other end of winding26 is connected through a resistor 27 and two rectifier units 28 and 30which in turn are connected in series with windings 31 and 32 on twolegs of a second core 33. The other ends of windings 31 and 32 areconnected directly to the ends of secondary winding 25 on transformer10.

The sensing portion of this circuit comprises a Wheatstone bridge 34which includes two resistors 35 and 36 and two lamps 37 and 38. Thebridge is supplied with power from the load terminals 15-23, thenegative terminal 15 being connected to the bottom of the bridge and thetop of the bridge being connected through an adjustable resistor and adirect current bias winding 41 to the positive terminal 23. Since theoutput voltage is regulated and is substantially constant the currentthrough the above mentioned circuit is also constant and the amount ofmagnetic fiux induced in the middle core is constant. The other twoterminals of the bridge 34 are connected to a control winding 42 on themiddle section of core 43, this winding comprising the point ofapplication of a control current due to a change in output voltageacross the load circuit.

For reasons that will be explained later it is desired that noalternating flux be present in the middle section of core 18 and toinsure that this condition exists a short circuited winding 43 is put onthis portion of the coil. Winding 43 may be an actual winding of threeor four turns of heavy copper wire or it may be a conductive sleevehaving only one turn and extending for the entire length of the coreportion.

The circuit described above is actually two stages of a magneticamplifier working from a bridge sensing circuit. In its usual embodimentthe circuit is very sensitive to small variations in the load circuitand since there is a slight time delay because of the inductancesinvolved the circuit would hunt if some provision were not made tocounteract the tendency. For this reason an anti-hunt winding 44 and isplaced on the central portion of each core 18 and 33. These windings areeach in series with a capacitor 46 and 47 which effectively eliminatesthe direct current available at the output terminals. Windings 44 and 45together with their capacitors 46 and 47 are connected across the outputterminals and receive only the sudden variations which are present atthe output terminals when the impedance of the load 24 is changedabruptly. The direction of the flux produced by windings 44 and 45 is inthe opposite direction to the flux produced by winding 26 on core 18 andwinding 42 on core 33 and therefore large transient values of flux whichotherwise would cause hunting are eliminated.

Fig. 2 shows one arrangement of cores which can be used by either one ofthe transformers in Fig. 1. Windings 16 and 17 can be positioned on theoutside core portions while windings 43, 26 and 41 are mounted on theother two legs which have been clamped together. The results will be thesame as those obtained by core 18.

The cores shown in Fig. 2 do not have to be clamped together and thearrangement shown in Fig. 3 may be employed where two circular cores and51 are used. The only connections between these cores are the windingssuch as 26 and 41 which enclose both cores.

The operation of the circuit shown in Fig. l is as follows: with anaverage voltage impressed on terminals 12, 13 and an unvarying load 24the power secondary winding 14 delivers current through windings 16 and17 to the two rectifiers 2t) and 21, thereby applying a r direct currentvoltage through filter circuit 22 to the load circuit 24. Also secondarywinding 25 applies a similar but much smaller current through windings31 and 32 in series with rectifier units and 30 to winding 26 on thecentral portion of core 18. The current through this winding produces anunvarying magnetic flux in core 18 which partially saturates it, alsothe current from the positive terminal 23 over conductor 52, throughcoil 41, through the bridge circuit 34, to the negative terminal 15 alsocontributes magnetic flux which helps to maintain core 18 in a partlysaturated condition. The short circuit winding 43 eliminates anyalternating flux components which may be introduced by winding 26. Aslong as there is no change in the output voltage there will be nocurrent through either one of the anti-hunt windings 44 and 45 andbecause of the unvarying output voltage there will be no change in thebridge circuit and therefore no change of magnetic flux in core 33 dueto winding 42.

Now let it be assumed that the load 24 is varied in value so as to causean increase in voltage across terminals 15, 23. This action causes anincrease in saturation of core 18 because of the increase of currentthrough windings 16 and 17. Also the saturation of core 33 is increasedbecause of current increase in coils 31 and 32, this increase in currentcommunicated to winding 26 on core 18 and causing a. further increase ofsaturation in that core. The voltage of the output terminals ismomentarily increased and this action causes more current to flow overconductor 52, through coil 41, through the bridge 34', and back to thenegative terminal 15. The lamp bridge 34 is normally unbalanced and asmall current flows from the bridge through winding 42 on the center legof core 33 and inducing a steady flux in the core. This flux due towinding 42 is opposed to the flux produced by windings 31 and 32. In asimilar manner the current through winding 26 produces a steady fluxwhich is opposed to the flux produced by winding 41 in series with thebridge circuit.

When the current is increased through the bridge circuit there is noappreciable change of resistance in resistors 35 and 36 but theresistance of lamps 37, 38 increases considerably and unbalances thebridge to a still greater extent sending a large increase in currentthrough coil 42 thereby lowering the saturation of core 33 andincreasing the reactance values of windings 31 and 32 and decreasing thecurrent through these coils and rectifier units 28 and 30 and therebylowering the current through winding 26 by a considerable amount. Thisaction causes a decrease in saturation of core 18 and an increase in thereactance values of windings 16 and 17 thereby increasing the voltagedrop across these windings and lowering the output voltage to itsprevious regulated value.

A decrease of the alternating current supply voltage produces changes incurrents and voltages which are opposite to the changes described above,the result being that the saturation of core 18 is increased, thereactance value of cores 16 and 17 are decreased, and the output voltageis raised to the desired regulated value.

The load capacity of core 18 and its associated load windings 16 and 17are considerably increased by the use of winding 41 which may bedescribed as a direct current bias coil. When normal current is flowingthrough windings 16 and 1'7 the magnetic flux produced by them issutficient to cause saturation of the core 18. The current through coil41 and the bridge circuit counteracts this flux and eliminates part ofthe saturating action. As described above the short circuited winding 43efiectively eliminates alternating magnetic flux from the center leg ofthe transformer core. The actions of the two anti-hunt circuits 44 and45 have been previously described.

The above description has been applied to shell type cores asillustrated in Fig. 1. However, any type of core such as those shown inFigs. 2 and 3 may be employed since the flux which is induced by coil 16lasts for only half of the alternating current cycle because thiswinding is in series with rectifier 20. The same is true of winding 17in series with rectifier 21, therefore the fluxes produced by these twocoils cannot occur at the same time and do not interact with each other.

The circuit shown in Fig. 4 is similar to the circuit shown in Fig. 1except that the short circuited coil 4-3 of Fig. 1 has been replaced byan A. C. bias coil 54 which is connected to a similar coil 55 on thecenter leg of core 33. Coil 54 is employed to reduce the alternatingcurrent flux in the center leg of core 13 by current derived from coil55 on the center leg of coil 33, this control of alternating fluxresulting in an improved regulating action and a more flexible system ascompared to the short circuited winding. The other operations connectedwith the circuit shown in Fig. 4 are the same as those described abovein connection with Fig. 1.

The following flux values may be used in the circuit shown in Fig. l andare illustrative of a specific application of the invention. A constantvalue of 24 ampere turns is applied by winding 42 on core 33 due to theunbalanced condition of the lamp bridge 34. The current through winding26 on core 18 appiles a variable flux to this core, the value of whichmay range from to 60 ampere turns. This magnetizing action opposes theaction of coil 41 which applies 24 ampere turns to the core.

While there have been described and illustrated specific embodiments ofthe invention, it will be obvious that various changes and modificationscan be made therein without departing from the field of the inventionwhich should be limited only by the scope of the appended claims.

We claim:

1. A voltage regulator for an alternating current supply circuitcomprising; a first magnetic core having two windings, each coupled tothe supply circuit and each in series with a rectifier which isconnected to one terminal of a load circuit; a connection between asecond terminal of the load circuit and a center voltage tap coupled tothe supply circuit; a second magnetic core having two windings, eachcoupled to the supply circuit and each in series with a rectifier whichis connected to one side of a control winding on the first magneticcore, the other side of the control winding connected to a centervoltage tap coupled to the supply circuit; a sensing circuit fordetermining voltage changes on the output terminals comprising a fourarm bridge, two of said arms comprising resistors whose resistancevalues do not vary with the current, and two of said arms comprisingmetallic filament lamps whose resistance varies considerably with thecurrent; two opposing junction points on the bridge connected to theoutput terminals in series with a winding on the first magnetic core;and two other opposing junction points on the bridge connected to acontrol winding on the second magnetic core.

2. A voltage regulator for an alternating current supply circuitcomprising; a first saturable magnetic core having two power windings,each coupled to the supply circuit and each connected in series with arectifier which is connected to one terminal of a direct current loadcircuit, the voltage of which is maintained at a constant predeterminedvalue; a connection between a second terminal of the load circuit and acenter voltage tap coupled to the supply circuit; a second saturablemagnetic core having two windings, each coupled to the supply circuitand each connected in series wtih a rectifier which is connected to oneend of a control winding on the first magnetic core, the other end ofthe control winding connected to a center voltage tap coupled to thesupply circuit, the current through said control winding for varying thesaturation of the first saturable core and varying the reactance valueof the two power windings on the first core; a sensing circuit forsensing voltage changes on the load terminals, said sensing circuitincluding a four arm bridge, two of said arms comprising resistors whoseresistance is invariable with the current, and two of said armscomprising metallic filament lamps whose resistance varies with thecurrent through them; said resistors connected opposite to each other inthe bridge circuit, and said lamps also connected opposite to eachother; two opposing junction points on the bridge connected to the loadterminals and the other two junction points connected to a controlwinding on the second magnetic core for causing variations in saturationof that core.

3. A voltage regulator for an alternating current supply circuitcomprising; a first saturable magnetic core having three legs, a firstand second leg of which are provided with power windings, each of saidpower windings coupled to the supply circuit and each connected inseries with a rectifier which is connected to one terminal of a directcurrent load circuit; a connection between a second terminal of the loadcircuit and a center voltage tap coupled to the supply circuit; a secondsaturable magnetic core having three legs, a first and second leg ofwhich are provided with windings which are coupled to the supply circuitand each connected in series with a rectifier which is connected to oneend of a control winding on the third leg of the first magnetic core,the other end of the control winding connected to a center voltage tapcoupled to the supply circuit; a sensing circuit for sensing voltagechanges on the load terminals, said sensing circuit including a four-armbridge, two of said arms comprising resistors whose resistance isinvariable with the current, and two of said arms comprising metallicfilament lamps whose resistance varies with the current through them;said resistors connected opposite to each other in the bridge circuit,and said lamps also connected opposite to each other; two opposingjunction points on the bridge connected to the load terminals and theother two junction points connected to a control winding on the thirdleg of the second magnetic core for causing variations in the saturationof that core when the output voltage varies.

4. A voltage regulator for an alternating current supply circuitcomprising; a first saturable magnetic core having three legs; a powerwinding on two of said legs, each of said power windings coupled to thesupply circuit and each connected in series with a rectifier which isconnected to one terminal of a direct current load circuit; a connectionbetween a second terminal of the load circuit and a center voltage tapcoupled to the supply circuit; a second saturable magnetic core havingthree legs; a winding on two of said legs, each of said windings coupledto the supply circuit and each connected in series with a rectifierwhich is connected to one end of a control winding on the third leg ofthe first magnetic core, the other end of the control winding connectedto a center voltage tap coupled to the supply circuit; a sensing circuitfor sensing voltage changes on the load terminals, said sensing circuitincluding a four-arm bridge, two of said arms comprising componentswhose resistance is substantially independent of the current passingthrough them, and two of said arms comprising components whoseresistance varies by a substantial amount when the current passingthrough them is changed, two opposing junction points on the bridgeconnected to the load terminals and the other two junction pointsconnected to a control winding on the third leg of the second magneticcore for causing variations in the saturation of the second core whenthe output voltage varies.

References Cited in the file of this patent UNITED STATES PATENTS

